1. Field of the Invention.
The invention relates to a method for the production of an assembled camshaft and a device for implementing said method.
2. Description of the Related Art
The U.S. Pat. No. 5,299,881 discloses an assembled camshaft, where the individual cams and the corresponding shaft are prefabricated in separate production steps, and then the cams are pushed in such a manner on the shaft by means of a special joining technology that there is a play-free fit between the shaft and the cams. Each prefabricated cam exhibits an inner bore and at least two axially separated annular zones, which are separated from one another by at least one free space, which is located in the inner bore of the cams. The space and the zones are symmetrical to the central plane of the cams. To manufacture the assembled camshaft, the individual cams are pushed onto the shaft so that the result is a fit between the said zones and the periphery of the shaft. One problem lies in the fact that it is relatively difficult and problematic to push the said cams on, in particular when the cams are pushed on or over the areas, where they are supposed to be fixed in position. In addition, the cams exhibit a relatively complicated design.
The object of the present invention is to provide a method for the production of assembled camshafts, by means of which the push-on operation of the cams onto the corresponding shaft is improved.
This problem is solved by means of a method for the production of an assembled camshaft where parts, in particular cams, are pushed by means of joining operations on a shaft into predetermined axial positions and specified circumferential positions with friction contact due to the fit connection. The cams in the thrust direction of the cams or the shaft, seen in its front face, exhibit a groove which surrounds the cam""s inner bore and which is designed essentially wedge-shaded and exhibits a linear or curved slope. running in the direction of the inner wall of the bore. When a cam is slid on the shaft into the predetermined axial position and optionally when the cam is rotated into the specified circumferential position, a lubricant is introduced into the groove serving as the lubricant groove, this lubricant being pulled continuously out of the groove into the inner bore of the cam during the push-on process.
The present invention further includes a joining device for implementing this method. The joining device includes a holding member with at least two rolls, which lie opposite one another and engage on the linear side faces of a cam and which can be forced by means of a force against the side faces, in order to orient the line of symmetry of the cam held in the holding member with respect to the line of symmetry between the opposing rolls, whereby then the rolls are opposite one another vertically to the line of symmetry of the cam.
The important advantage of the present invention lies in the fact that the pushing of the individual cams onto the shaft is facilitated significantly by means of a front wedge-shaped lubricant groove or chamfer, provided in the area of the inner bore of the cams in the push-on direction, because lubricant, introduced into this lubricant groove, is pulled continuously into the inner bore of the groove during the push-on process as a consequence of the wedge-shaped design of the groove, so that the friction between the outer circumference of the shaft and the inner circumference of the inner bore of the groove is significantly reduced. When a cam is pushed onto the shaft, it can also be easily rotated in an advantageous manner into the predetermined peripheral position due to the aforementioned lubrication through the wedge-shaped groove. In an advantageous design of the invention, there is not only the front lubricant groove but also other lubricant grooves on the inside of the cam, and in particular not symmetrical to the central plane of the cam. The shape of the wedge-shaped lubricant grooves is optimal.
According to preferred embodiments of the method, the groove may have in essence a wedge shape and exhibit a slope, which runs linearly or curved in the direction of the inner wall of the bore. This groove forms an approach slope when introducing the shaft into the inner bore of the cam. At least one other lubricant groove may be included, in addition to the lubricant groove. The lubricant groove and the at least one other lubricant groove may be designed identically or may differ with respect to the angle of their slopes and/or with respect to their widths.
According to further embodiments of the method, the shaft can exhibit, in the area of the predetermined axial positions of the cams, fixing areas with a diameter which is larger with respect to the other outside diameter of the shaft, whereby the grooves of the cams form an approach slope when the cams are slid onto the fixing areas. The fixing areas may exhibit an approach slope at least on their side facing the cam during the push-on operation.
As a further embodiment of the method, a lubricant may be introduced into the lubricant groove during the joining operation. This lubricant can be treated in such a manner selectively after the joining operation that it loses its friction-reducing function. Such loss of its friction-reducing function after the joining operation may be due to the heating up of the assembled camshaft.
According to preferred embodiments of the joining device for implementing the method, two additional opposing rolls may engage on the cylindrical periphery of the cam below the first two rolls. The holding member can exhibit an axial thrust bearing, which allows the cam to be rotated into the specified circumferential position prior to the execution of a relative motion between the holding member and the shaft or during or after the execution of the relative motion. The axial thrust bearing exhibits in the circumferential direction over a circular arc uniformly distributed depressions, in which there are roller bodies, whose sides facing the cam project beyond the side of the holding member facing the cam and rest against the side of the cam facing the holding member. These roller bodies may be embodied as balls.
According to further preferred embodiments, the joining device may exhibit a plurality of cams, which are held in holding members in the circumferential direction in specified positions and in the axial direction in predetermined positions, whereby holding members with the cams are pushed onto the shaft in one operation or the shaft is pushed into the cams in one operation.
The invention and its embodiments are explained in detail below in conjunction with the figures.